The primary objective of the study is to determine the effects of Interleukin-10 on the Cytochrome P450 enzymes 1A1/2, 2D6, 3A4, and 2C8/9 using the metabolic products of caffeine, dextromethorphan, midazolam, and tolbutamide as markers. The secondary objective is to evaluate the safety and tolerance of IL-10 when administered as a subcutaneous injection a daily for a six day period at a dose of 8ug/kg. Up to 12 healthy, non- smoking, 18-45 year old males will complete this randomized, double-blind, multiple dose, two period crossover pharmacokinetic study. On Day 1 dubjects will be hospitalized and randomized for the crossover order of receiving IL-10 or placebo. The patient will receive either the IL-10 or placebo by subcutaneous injection on days 1-6. The subjects will receive IL-10 for the duration of an entire treatment period and will receive the placebo for the duration of an entire treatment period as outlined in the randomization schedule. On day 4 of both treatment periods tolbutamide, caffeine, and dextrohethorphan will be administered orally. On day 5 of both treatment periods midazolam will be administered by IV infusion. The morning of Day 7 patients will be discharged from the hospital. Following at least a 14 day washout period the patient will return for the second treatment period which will be identical to the first. The patient will again return on day 29 of treatment period two to have a blood sample drawn.